This invention relates to an apparatus for sensing rotational speed and a method for monitoring rotational speed. It is established art to use a combination stator and relatively rotatable reluctor, each having coacting portions, so related that they will effect a predetermined change in reluctance when one portion rotates or moves past a cooperating part of the other. Generally speaking, the functional portions of a relatively rotatable reluctor and stator can be in the form of protuberances or points which cause a change in flux density as they move one past the other, and effected by this change in flux density is the generation of a voltage output because the two parts, one moving past the other, serve as a generator that develops a voltage output. This voltage output occurs as an alternating voltage output and the frequency of the alternating voltage is a direct measure of rotational speed of either a drive shaft or other member rotating the reluctor. The amplitude and frequency of the voltage are the significant parameters utilized in calculating the rotational speed of the reluctor. However, these expedients do not relate or address the problem of how to obtain a speed sensor which can accommodate for relative movement, particularly in a radial direction, between the reluctor and the stator without disturbing the value of the voltage output at various positions of the reluctor relative to the stator. Heretofore the conventional constructions demanded manufacturing tolerances which would not permit a high a degree of relative axial an radial movements between the reluctor and the stator without introducing a false signal for adversely affecting the voltage output. Also, in previous devices it was necessary to maintain the air gap between the relatively rotatable or movable member and the stationary member within well defined tolerances. To the degree that those tolerances had to be maintained within close limitations, this added materially to the cost of the device, and to the extent that the tolerances were not maintainable, certain factors of error were introduced in the readout because of a change in the amplitude of the voltage output which made it more difficult to monitor consistently.
In the assembly of sensor devices of the type described, what has long been needed is a quick and efficient way of mounting the sensor and obviate the need for such devices as jam nuts, E-rings, threads, and the like. What the present invention comprises is a housing device which has an integrally constructed or an insert molded mounting ring disposed at the open end of the housing and after the sensor is assembled and mounted within a coacting housing the combination is simply press fitted through the mounting ring within a companion opening of a complementary housing. Overall, it is intended in the present invention to provide a rotational speed sensor and method for monitoring rotational speed wherein the air gaps which are an essential feature of any magnetic speed sensor, are much larger because the combination of reluctor and stator develops a greater voltage amplitude and is less affected by air gaps magnitude and variations. Because of this greater degree of voltage amplitude output, it is possible to tolerate greater air gaps and greater variation of air gaps without compromising or preventing a readily readable voltage output. All of this contributes to the manufacturing and assembly of a highly reliable rotational speed sensor; one which is easily assembled, is relatively free from readout error, is inherently more readable itself, and can be easily mounted upon a companion structure such as a vacuum pump or other adjacent structure.